The present disclosure relates to a sheet feed device in which a recording medium housing cassette for housing a sheet-shaped recording medium is drawably mounted and that is used in a copy machine, a printer, a facsimile, or the like, and relates particularly to a configuration that prevents a sheet from being damaged when the recording medium housing cassette is drawn out or a roller from being deformed after storage for a long time.
Conventionally, an image forming apparatus such as a copy machine, a printer, or a facsimile has a configuration in which, at a bottom portion of a main body of the apparatus, a paper feed cassette for housing a plurality of paper sheets (recording media) is provided so as to be drawable from the main body of the image forming apparatus. By a feed-out unit composed of a pick-up roller and so on and a separation conveyance unit composed of a paper feed roller and so on, which are provided above the paper feed cassette, the paper sheets housed in the paper feed cassette are fed out one by one in order, and by a conveyance roller, each of the paper sheets thus fed out is conveyed to an image forming portion and a fixing portion so that an image is formed thereon.
The configuration described above has been disadvantageous in that, when, in a state where a paper sheet is nipped by the separation conveyance unit, the paper feed cassette is drawn out from the main body of the image forming apparatus, there is a possibility that the paper sheet is damaged such as being torn or flawed. There has thus been proposed a method for preventing a paper sheet from being torn or flawed when a paper feed cassette is drawn out, and there is known, for example, a paper feed device in which, by a nip release member that moves, in coordination with an operation of drawing out/inserting a paper feed tray, in a direction orthogonal to a direction in which the paper feed tray is drawn out/inserted, a feed-out roller is separated from a paper sheet, and a pressure contact state between rollers constituting a dispensing conveyance roller pair is released.
In this configuration, in a state where the paper feed tray has been inserted, the rollers constituting the dispensing conveyance roller pair are in a pressure contact state with each other, and in a state where the paper feed tray has been drawn out, the pressure contact state between the rollers constituting the roller pair is released. Because of this, there occurs a time lag, albeit of short duration, between a time when drawing out of the paper feed tray is started and a time when the pressure contact state between the rollers constituting the dispensing conveyance roller pair is released. Hence, immediately after drawing out of the paper feed tray is started, a paper sheet is pulled in a state of being nipped between the rollers constituting the dispensing conveyance roller pair, which has rendered it impossible to completely prevent damage to paper sheets.
Furthermore, in a case where the image forming apparatus is kept in storage for along time in a state where the paper feed tray is inserted therein, a pressure contact state between the rollers constituting the dispensing conveyance roller pair is kept for a long time, which also has led to a problem that a feed roller (feed member) or a retard roller (separation member), which constitute the dispensing conveyance roller pair, is deformed due to a contact pressure therebetween.